Abstract 1827: Inhibition of Src, HER2, and EGFR by the multi-kinase inhibitor KD019 overcomes trastuzumab resistance in breast cancer

Abstract

Abstract KD019 (previously EXEL-7647) is an orally bioavailable spectrum selective small molecule kinase inhibitor of Src family nonreceptor tyrosine kinases (Src) as well as HER2, EGFR, and VEGFR2/KDR. Because of its complement of targets KD019 is able to disrupt multiple components of tumor pathology and, in earlier studies, KD019 demonstrated robust activity in multiple in vivo tumor models. In recent years Src has emerged as a critical convergent node downstream of multiple signaling cascades initiated by transmembrane receptor tyrosine kinases (RTKs), most notably HER2, EGFR and IGF-1R. Crosstalk between Src and RTKs facilitates RTK-dependent tumor growth and, in patients with HER2-amplified (HER2+) breast cancer, where Src is upregulated, may confer resistance to anti-HER2 therapies. Based on the target specificity of KD019, including Src, we hypothesized that KD019 may prove to be an effective treatment in overcoming trastuzumab resistance in HER2+ breast cancer. Here we present data showing that KD019 effectively inhibited growth of several trastuzumab resistant cell lines with IC50 of 0.3 uM in vitro. Not only did KD019 potently inhibit HER2 and EGFR phosphorylation in these cells, but it also efficiently inhibited the phosphorylation of c-Met through receptor hetero-oligomerization mechanism, thus downregulating another pathway by which tumors may escape HER2 targeted therapies. Further, we demonstrate that once daily dosing of KD019 strongly inhibited tumor growth in xenograft models of trastuzumab resistance and that Src activity was inhibited in KD019 treated tumors even 24 hrs after drug administration. The significance of inhibiting the specific combination of targets is underscored by the fact that KD019 was 10 fold more potent when compared to saracatinib (a selective Src inhibitor) in inhibiting growth of trastuzumab resistant cells, which are also insensitive to blockade of individual RTKs. Together, these results provide a rational for clinical investigation of KD019 in patients whose tumors are resistant to anti-HER2 therapies. Citation Format: Rigen Mo, Nishta Rao, James Tonra, Samuel Waksal, Masha Poyurovsky. Inhibition of Src, HER2, and EGFR by the multi-kinase inhibitor KD019 overcomes trastuzumab resistance in breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1827. doi:10.1158/1538-7445.AM2014-1827